Referring to FIG. 1 of the drawings, prior art trailer couplings have a drawbar 10 with an eye 12 at the end. The drawbar is attached to the trailer and the eye fits over the pintle of a hitch which is attached to the tractor or a lead trailer. The drawbar is loaded relative to the trailer in one direction when the trailer is being pulled by the tractor or a lead trailer, and in particular when the tractor is accelerating. The drawbar is loaded in the opposite direction when the tractor is decelerating. In order to cushion this loading and unloading the drawbar is mounted in a housing 14 which is attached to the trailer. The housing has an outer cylindrical chamber which opens out of the front of the housing and an inner cylindrical chamber which opens out of the rear of the housing. The inner and outer chambers are separated from one another by a partial wall 18. The chambers have elastomeric bushings located in them. A first bushing 16a cushions movement of the drawbar when the drawbar is being pushed toward the trailer, and a second bushing 16b cushions movement of the drawbar when the drawbar is being pulled away from the trailer.
Referring now to FIG. 2, the second bushing 16b extends between the wall 18 and a metal washer 20 which is attached to the threaded end of the drawbar by a nut 22. In the prior art couplings the second bushing must extend out of the housing sufficiently that the washer never enters the housing because a metal washer will damage the housing and a metal washer is necessary to withstand the action of the nut being tightened on the drawbar and provide adequate surface area to contact the entire outer face of the bushing.
Referring now to FIG. 2a, because the second bushing 16b extends out of the housing 14, when the second bushing 16b is compressed a portion of it bulges out of the gap between the housing and the washer, A. With repeated loading this portion of the bushing prematurely wears out. Likewise, the other end of the second bushing bulges between the partial wall 18 and the central drawbar rod 23, B. This also causes the bushing to prematurely wear out.